a. The Field of the Invention
This invention is concerned in general with the formation of traffic regulating markings on roadway pavements or other roadable surfaces such as traffic lane dividing and/or lane edge forming lines the direction of which generally corresponds with that of usual movement of the vehicle along the road.
More particularly the present invention is concerned with forming of traffic regulating marking including in the marking defining surface area retro reflecting elements adapted to provide retro reflection of the light beams irradiated by the vehicles headlamps in night time and/or the visibility is prejudiced by the weather.
Said retro reflecting elements concerned with the invention are secured to the road pavement by means of a carrying layer which can be formed of a paint, a resinous layer of a prefabricated tape material adapted to be laid on and adhesively secured to the road pavement generally by means of an intermediate primer layer. The layers to which the retro reflecting elements are secured to the road pavement are known in the art and do not individually form characteristics of the invention, and provided that the retro reflecting elements are properly positioned and firmly secured to the road pavement, the road pavement, the layer with which said elements are associated will be encompassed within the definition "carrying or anchoring layer" herein below.
b. The Prior Art
The art of forming traffic regulating signs including retro reflecting generally globular elements is known and worked one, and extensive comments thereabout are unnecessary. The arrangement and the principles of such retro reflecting elements have been disclosed for example in the U.S. Pat. Nos. 3,964,821 and 4,049,337 granted to the instant applicant. A particularly advantageous retro reflective element has been disclosed in another applicant's U.S. Pat. No. 4,072,403.
Generally speaking, the visibility at distance of the retro reflective elements in service, on a given surface area, and assuming that the elements consistently protrude above the surface of the actual carrying layer, is proportional to the density of same elements, that is to the number of elements circumscribed within a definite area. The brilliancy of the marking, in response to light beams irradiated by a vehicle headlamp, is grossly proportional to the density of elements.
On the other hand element density must not go over or under certain limits, even disregarding the cost, taking principally into account the following consideration.
(a) as discussed in the above referred U.S. Pat. Nos. 3,964,821 and 4,049,337 such elements are impinged by grazing light, that is by rays forming a small angle to the road pavement;
(b) the elements protrude above the surface of the marking for a noticeable height, such as from 1 mm to 6 mm, preferably of 2 or 3 mm approx. Therefore, when impinged by grazing light, each element forms a shadow which covers a part of the marked area;
(c) when the shadow covers part of the following element, this element is proportionally disactivated; when the shadow leaves too much uncovered area the brilliancy is proportionally damaged;
(d) the marking forms itself a part of the roadable surface which must be non-skidding and therefore the element density must be such as to not provide a skiddish surface; this latter feature is important in the direction of travel, which corresponds to light impingement. Safe adherence is essential during accelerations, emergency brakings and the like. Therefore the elements must be so spaced to provide good adherence in the interspaces in the direction of travel.
In the U.S. Pat. No. 4,069,281 (in particular FIGS. 6 and 11) the applicant has proposed specifically to arrange for marking tapes in resin protrusion and reflective elements in rows perpendicular to the lane marking, that means perpendicular to the grazing light impingement. It was not clear at the time the importance for the maximum brilliancy to have all the reflective elements exactly positioned and aligned in rows, that means to have these elements prealigned because applying the same to the marking material and the rows exactly spaced one from the other.